This invention relates generally to the structure of shoes. More specifically, this invention relates to the structure of running shoes. Still more particularly, this invention relates to variations in the structure of such shoes having a sole contour which follows a theoretically ideal stability plane as a basic concept, but which deviates therefrom outwardly, to provide greater than natural stability. Still more particularly, this invention relates to the use of structures approximating, but increasing beyond, a theoretically ideal stability plane to provide greater than natural stability for an individual whose natural foot and ankle biomechanical functioning have been degraded by a lifetime use of flawed existing shoes.
Existing running shoes are unnecessarily unsafe. They seriously disrupt natural human biomechanics. The resulting unnatural foot and ankle motion leads to what are abnormally high levels of running injuries.
Proof of the unnatural effect of shoes has come quite unexpectedly from the discovery that, at the extreme end of its normal range of motion, the unshod bare foot is naturally stable, almost unsprainable, while the foot equipped with any shoe, athletic or otherwise, is artificially unstable and abnormally prone to ankle sprains. Consequently, ordinary ankle sprains must be viewed as largely an unnatural phenomena, even though fairly common. Compelling evidence demonstrates that the stability of bare feet is entirely different from the stability of shoe-equipped feet.
The underlying cause of the universal instability of shoes is a critical but correctable design flaw. That hidden flaw, so deeply ingrained in existing shoe designs, is so extraordinarily fundamental that it has remained unnoticed until now. The flaw is revealed by a novel new biomechanical test, one that is unprecedented in its simplicity. The test simulates a lateral ankle sprain while standing stationary. It is easy enough to be duplicated and verified by anyone; it only takes a few minutes and requires no scientific equipment or expertise.
The simplicity of the test belies its surprisingly convincing results. It demonstrates an obvious difference in stability between a bare foot and a running shoe, a difference so unexpectedly huge that it makes an apparently subjective test clearly objective instead. The test proves beyond doubt that all existing shoes are unsafely unstable.
The broader implication of this uniquely unambiguous discovery are potentially far-reaching. The same fundamental flaw in existing shoes that is glaringly exposed by the new test also appears to be the major cause of chronic overuse injuries, which are unusually common in running, as well as other sport injuries. It causes the chronic injuries in the same way it causes ankle sprains; that is, by seriously disrupting natural foot and ankle biomechanics.
The applicant has introduced into the art the concept of a theoretically ideal stability plane as a structural basis for shoe sole designs. That concept as implemented into shoes such as street shoes and athletic shoes is presented in U.S. Pat. No. 4,989,349, issued Feb. 5, 1991, U.S. Pat. No. 5,317,819, issued Jun. 7, 1994, and Ser. No. 07/400,714, filed an Aug. 30, 1989, well as in PCT Application No. PCT/US89/03076 filed on Jul. 14, 1989. The purpose of the theoretically ideal stability plane as described in these applications was primarily to provide a neutral design that allows for natural foot and ankle biomechanics as close as possible to that between the foot and the ground, and to avoid-the serious interference with natural foot and ankle biomechanics inherent in existing shoes.
This new invention is a modification of the inventions disclosed and claimed in the earlier applications and develops the application of the concept of the theoretically ideal stability plane to other shoe structures. As such, it presents certain structural ideas which deviate outwardly from the theoretically ideal stability plane to compensate for faulty foot biomechanics caused by the major flaw in existing shoe designs identified in the earlier patent applications.
The shoe sole designs in this application are based on a recognition that lifetime use of existing shoes, the unnatural design of which is innately and seriously flawed, has produced actual structural changes in the human foot and ankle. Existing shoes thereby have altered natural human biomechanics in many, if not most, individuals to an extent that must be compensated for in an enhanced and therapeutic design. The continual repetition of serious interference by existing shoes appears to have produced individual biomechanical changes that may be permanent,so simply removing the cause is not enough. Treating the residual effect must also be undertaken.
Accordingly, it is a general object of this invention to elaborate upon the application of the principle of the theoretically ideal stability plane to other shoe structures.
It is still another object of this invention to provide a shoe having a sole contour which deviates outwardly in a constructive way from the theoretically ideal stability plane.
It is another object of this invention to provide a sole contour having a shape naturally contoured to the shape of a human foot, but having a shoe sole thickness which is increases somewhat beyond the thickness specified by the theoretically ideal stability plane.
It is another object of this invention to provide a naturally contoured shoe sole having a thickness somewhat greater than mandated by the concept of a theoretically ideal stability plane, either through most of the contour of the sole, or at preselected portions of the sole.
It is yet another object of this invention to provide a naturally contoured shoe sole having a thickness which approximates a theoretically ideal stability plane, but which varies toward either a greater thickness throughout the sole or at spaced portions thereof, or toward a similar but lesser thickness.
These and other objects of the invention will become apparent from a detailed description of the invention which follows taken with the accompanying drawings.
Directed to achieving the aforementioned objects and to overcoming problems with prior art shoes, a shoe according to the invention comprises a sole having at least a portion thereof following approximately the contour of a theoretically ideal stability plane, preferably applied to a naturally contoured shoe sole approximating the contour of a human foot.
In another aspect, the shoe includes a naturally contoured sole structure exhibiting natural deformation which closely parallels the natural deformation of a foot under the same load, and having a contour which approximates, but increases beyond the theoretically ideal stability plane. When the shoe sole thickness is increased beyond the theoretically ideal stability plane, greater than natural stability results; when thickness is decreased, greater than natural motion results.
In a preferred embodiment, such variations are consistent through all frontal plane cross sections so that there are proportionally equal increases to the theoretically ideal stability plane from front to back as the shoe sole thickness increases from the forefoot area to the heel area, as do most existing shoes, when measured in sagittal plane cross sections. In alternative embodiments, the thickness may increase, then decrease at respective adjacent locations, or vary in other thickness sequences.
The thickness variations may be symmetrical on both sides, or asymmetrical, particularly since it may be desirable to provide greater stability for the medial side than the lateral side to compensate for common pronation problems. The variation pattern of the right shoe can vary from that of the left shoe. Variation in shoe sole density or bottom sole tread can also provide reduced but similar effects.
These and other features of the invention will become apparent from the detailed description of the invention which follows.